1. Field of the Invention
The present invention relates to acrylic multilayer polymer powders. Specifically, it relates to acrylic multilayer polymer powders with excellent drying properties, which contain coagulated powder obtained from the polymer latex of an emulsion polymer.
2. Description of the Related Art
Methacrylic resins, while having excellent weather resistance, luster and transparency also have the disadvantage of low impact resistance, which has led to a desire for their improvement. The introduction of acrylic elastomers thereto is an effective means of imparting impact resistance while maintaining weather resistance, and there have hitherto been known methods of blending rubber polymer/rigid polymer double layer polymers and semi-rubber polymer/rubber polymer/rigid polymer triple-layer polymers (U.S. Pat. No. 3,808,180, No. 3,843,753 and No. 4,730,023 and Japanese Unexamined Patent Publication No. 62-230841).
In these methods, in order to impart impact resistance to the methacrylic resin without sacrificing its original luster and transparency, it is necessary to reduce the proportion of the rubber components such as alkyl acrylate, and raise the relative proportion of rigid monomer components such as alkyl methacrylate ester in the multilayer polymer. The rubber component has a greater variation in the refractive index due to heat, so that the optical properties tends to be thus impaired by heat changes when the proportion of the rubber component portion becomes high. Consequently, such multilayer polymers are inevitably rigid, and have melting points exceeding 235.degree. C. which is considered relatively high.
On the other hand, multilayer polymers are generally produced by emulsion polymerization, after coagulation of the emulsified latex, via dehydration and drying. Here, in the case of rigid multilayer polymers with relatively high melting points, fusion between the polymer particles in the latex during coagulation does not easily occur, and the water content of the polymers recovered in the wet state tends to become relatively high. As a result, a large amount of heat is required for drying when a press dehydration extruder or fluidized drier is used, which leads to problems such as lower drying efficiency and increased product cost.